1. Field of the Invention
The field of this invention is within the printing art, specifically impact printing. More specifically, it is within the field of printing that relies upon hammers that are released from a hammerbank such as in a line printer. These hammers impact a ribbon against media that is to be printed upon that is in turn supported for impact against a platen. More particularly, it relates to the platen which is impacted by the hammers of the printer.
2. Description of the Prior Art
Prior art impact printers such as line matrix printers often employ a hard non-resilient non-elastic platen. This platen is impacted by hammers that are fired from a hammerbank having tips. The tips specifically impact a ribbon and paper or other media between the tips and the platen.
On the other hand some platens are made of an elastomeric material.
The foregoing hard platens create very high impact forces to the hammerspring that is released and fired against the platen and the intervening ribbon. Due to the high stiffness or modulus of the hammersprings, a very high impact force is encountered by the platen and ribbon.
Ribbons tend to deteriorate rapidly due to the fact that the tips of the hammers forming the dot matrix patterns apply great loads on the ribbon as they impact against the ribbon, paper or media, and platen against which they are supported. This ribbon deterioration can sometimes take place substantially before the normal ink life of a ribbon.
The deterioration factor is caused by these high impact forces continually and permanently flattening the threads of the ribbon. Eventually, these threads break and cause ribbon wear and in a worse case snagging.
The high stiffness of the platen and impacting print hammers impart substantial vibration and vibrational amplitudes in the hammerspring that limits the rate of firing. This tends to limit and diminish the uniformity of print densities from dot impact to another respective dot impact. The rate and quality of the printing is constrained by the material of the platen being of a hard non-forgiving metal. As can be appreciated, the vibrational modes and bounce effect of the hammers against the stiff hard platen create inconsistencies in printing thereby providing inconsistencies in not only appearance but accuracy in such items such as bar codes.
Other prior art platens employ a rubber or elastomeric platen. The impact forces generated by the small tips of the hammers are so high in these cases that the compressive fatigue strength of the rubber and its elastomeric nature is exceeded. During printing for a number of hours a rubber or elastomeric platen experiences a permanent deformation under the tips. This tends to change the print quality and overall ability of maintaining the net result of trying to protect the ribbon and diminish vibrational modes. Further to this extent, such rubber platens experience wear by the continual rubbing of the paper. The paper also has a drag applied to it. Summarily, the net result is that the platen experiences an excessive wear and compression factor.
This invention solves the foregoing drawbacks of the prior art by an inventive use of two basic components that are placed on the platen. These are formed by an elastomer and tiny ceramic balls, metallic balls, or hard material particles toward the surface of the elastomer. This combination provides an exterior band or cross-sectional depth of non-wearing very hard tiny hard ceramic, metallic spheres, powder or particles. These spheres, particles, or powder next to the surface of the elastomer function to overcome many of the wear and impact deficiencies of the prior art as enunciated hereinbefore.
One of the enhancements is the media or paper rubbing on the hard ceramic, metallic balls, or particles does not excessively wear the elastomeric material. Furthermore, the combination of hardened balls, powder or particles on the surface and elastomeric material surrounding them, allows a reduction in compressive forces. The result is the elastomeric material does not tend to break down as in the prior art. These advantages and other features of this invention will be readily seen as described hereinafter in the specification and related claims.